When a vehicle is on a graded surface, the vehicle experiences a gravitational force component that acts to move the vehicle in a generally downward direction, which may be in a direction opposite to the direction the vehicle driver wants the vehicle to move. For example, if the vehicle is moving up a graded surface or hill, in either a forward or a rearward direction, a gravitational force component will act in the opposite direction, tending to counteract the torque supplied by the vehicle powertrain. Thus, as many vehicle drivers have experienced, when moving a vehicle up a graded surface, the torque output from the vehicle powertrain typically needs to be increased in order to maintain the vehicle at the same speed on the graded surface as the vehicle had on a generally flat, or non-graded, surface.
In addition, if a vehicle driver wants to maintain the vehicle at a substantially stationary position (e.g., substantially zero speed) on a graded surface, the driver can do any one of several things. For example, the driver can apply the brakes or other brake command device, such as hand control, etc., or place the vehicle transmission shifter (if so equipped) in, for example, the “PARK” position. Alternately, in case of a manual transmission, the transmission can be locked in first gear with the parking brake applied to hold the vehicle on a grade. Yet another method that some drivers employ to maintain the vehicle at a substantially zero speed on a graded surface is to request that the powertrain supply a torque that is equal and opposite the gravitational force component. Typically, this torque request is provided by the vehicle driver pressing the vehicle “accelerator pedal” or “throttle pedal.”
Using the powertrain to supply a torque that is equal and opposite the gravitational force component can be, in many instances, used successfully to maintain a vehicle position on a graded surface. However, this method can result in powertrain component damage and/or reduce the lifetime of the powertrain and/or its components. For example, the torque converter in an automatic transmission-equipped vehicle, or the clutch in case of a manual transmission, can generate heat that may be of a magnitude sufficient to cause damage to the powertrain if this condition is maintained for a relatively long period of time. Moreover, in a vehicle powered by an electric motor, the motor may draw a so-called “stall current,” which can result in excessive heat generation, unnecessary power consumption, and potential component damage.
Accordingly, it is desirable to provide a system and method that can determine when vehicle powertrain torque is being used to substantially maintain a vehicle at a substantially zero speed on a graded surface, and to shift the supplied torque from the powertrain to another vehicle system or component such as the vehicle brake system. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.